Methods for Hybrid Wafer Bonding Integrated with CMOS Processing

ABSTRACT

Methods for forming an integrated device using CMOS processing with wafer bonding. In an embodiment, a method is disclosed that includes defining an integrated circuit function using a front-end substrate having one or more active devices and a back-end substrate having connections formed in metal layers in dielectric material, wherein the back-end substrate is free from active devices; manufacturing the front-end substrate in a first semiconductor process; more or less simultaneously, manufacturing the back-end substrate in a second semiconductor process; physically contacting bonding surfaces of the front-end substrate and the back-end substrate; and performing wafer bonding to form bonds between the front-end and back-end substrates to form an integrated circuit. Additional methods are disclosed.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a division of U.S. patent application Ser. No.13/903,700, entitled, “Methods for Hybrid Wafer Bonding Integrated withCMOS Processing,” filed on May 28, 2013, which application is related toU.S. Provisional Patent No. 61/793,766, Attorney Docket No. TSM13-0210P,filed Mar. 15, 2013, entitled “Methods for Hybrid Wafer Bonding,” and toU.S. Provisional Patent No. 61/798,664, Attorney Docket No. TSM13-0233P,filed Mar. 15, 2013, entitled “Methods for Hybrid Wafer BondingIntegrated with CMOS Processing,” which applications are herebyincorporated herein by reference in their entirety.

TECHNICAL FIELD

The embodiments relate generally to the use of bonding betweensubstrates, which include but are not limited to semiconductor wafers.The use of the bonding methods is applicable to a variety of deviceswhere two substrates are bonded.

BACKGROUND

Recent improvements for substrate to substrate or wafer bonding areincreasingly important in 3D IC structures. Wafer bonding isincreasingly used to provide increased integration by forming verticalstacks of semiconductor devices without the need for interveningstructures such as substrates or circuit boards. By bonding wafersdirectly, a single packaged integrated circuit may be produced whichincludes two or more wafer layers, providing increased system on a chipcapabilities. In one particular application of wafer bonding, an arrayof image sensors is formed on one wafer and bonded to an image sensorcircuit wafer, to provide an integrated image sensor system in a singlepackaged device.

Wafer to wafer bonding approaches known previously include oxide-oxideor fusion bonding, and metal to metal bonding using thermocompressionbonding at higher pressure and high temperatures. These prior approachesinduce high mechanical and thermal stress on the devices, or fail toprovide needed metal-to-metal connections.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the illustrative embodimentsdescribed herein and the advantages thereof, reference is now made tothe following descriptions taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 illustrates in a cross-sectional view a portion of a substrateincluding an advanced integrated circuit structure, used to illustratethe embodiments;

FIG. 2 illustrates in a cross-sectional view a front-end substrate ofthe embodiments;

FIG. 3 illustrates in a cross-sectional view a back-end substrate of theembodiments;

FIG. 4 illustrates in a cross-sectional view the front-end and back-endsubstrates of the embodiments in a wafer bonding process;

FIG. 5 illustrates in another cross-sectional view an integrated circuitstructure formed by the bonding process of FIG. 4;

FIG. 6 illustrates in another cross-sectional view a front-end substrateof an alternative embodiment;

FIG. 7 illustrates in a cross-sectional view a back-end substrate of thealternative embodiment of FIG. 6;

FIG. 8 illustrates in a cross-sectional view an embodiment integratedcircuit structure formed buy bonding the front-end substrate of FIG. 6and the back-end substrate of FIG. 7; and

FIG. 9 illustrates in a simplified flow diagram the steps of a methodembodiment.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION

The making and using of example illustrative embodiments are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the variousembodiments, and do not limit the scope of the specification, or theappended claims.

The use of wafer bonding to provide higher integration in semiconductordevices by producing 3D devices is increasing. As described in therelated application entitled “Methods for Hybrid Wafer Bonding,” theembodiments of the related application which is incorporated herein byreference above provide methods for metal pad to metal pad bonding withrobust connections at the interface between two substrates.

In advanced semiconductor process nodes, cycle time for CMOS integratedcircuits produced using multiple layers of metallization are increasing.Recently, cycle times for an advanced semiconductor process usingmultiple levels of metal may be from 4-8 weeks. As the minimum featuresizes of the semiconductor processes continue to shrink, thecomplexities of manufacturing these devices is increasing, which resultsin further increases in cycle time. Problems with defects also becomemore acute as the devices being manufactured become ever smaller. Forexample, plasma treatments of layers being formed above a semiconductorsubstrate may lead to plasma induced defects (PID) problems in thelayers previously formed, reducing yield.

Semiconductor manufacturing processes for forming active devices such asmetal-oxide-semiconductor FET devices are classified as “front-end-ofthe-line” (FEOL) or “front-end”and “back-end-of-the-line” (BEOL) or“back-end” processes. Front-end processes include doping regions by ionimplantation including well implants to form n and p regions in asubstrate, shallow trench isolation or LOCOS isolation to device activeareas for devices, forming gate structures including deposition of gatedielectrics and forming gate conductors, forming source and drainregions including ion implantation and thermal diffusion, formingsubstrate contacts, and continuing up to but not including the formationof the first level of metal (metal-1).

Back-end processes include forming interconnections (“wiring”) betweenthe active devices. The interconnections are formed using insulatinglayers and forming metal conductors in metal layers, with contactsconnecting the first layer of metal to the substrate or polysilicon, andconductive vias forming vertical connections between layers of metal.Current advanced processes may include 10 or more metallization layers.The back-end processes continue through terminals, usually called bondpads, formed in a passivation layer that provide the external connectorsto the wiring and thus to the integrated circuit. Packaging may beformed in the back-end process including passivation layers, and moldingoperations for example. Solder balls or bumps, bond wires, flip chipconnections or the like may be used to connect the completed devices toa circuit board or substrate.

In various embodiments, the front-end and back-end processes areperformed more or less simultaneously, or contemporaneously, and inparallel, saving cycle time. Further, the manufacture of the front-endsubstrate is performed without the need for performing multiple back-endprocesses on the front-end substrate, reducing PID defects or otherdamage defects on the active devices in the front-end substrate.

In an alternative embodiment, the front-end substrate and the back-endsubstrate each include a redistribution layer (RDL) which forms abonding interface. The RDL includes metal pads in an insulating layer.Fusion bonding, hybrid bonding or thermocompressive bonding is used toform metal pad to metal pad bonds between the RDL on the front-endsubstrate and the corresponding RDL on the back-end substrate.

In various embodiments, manufacturing cycle time is reduced by applyingwafer bonding to the problem of producing advanced CMOS integratedcircuits. In producing the CMOS integrated circuits, the methodembodiments include forming a device wafer or substrate including activetransistors processed only in front-end processes (the “front-endsubstrate”), and a second substrate or wafer having metal layers formingconnections corresponding to the active transistors formed in back-endprocesses, but not having any active devices requiring front endprocessing (the “back-end substrate”). The front-end and back-endsubstrates are processed separately. In an embodiment, the front-end andback-end substrates are processed in parallel, saving cycle time. Thefront-end and back-end substrates are then wafer bonded to form a devicestructure. In an embodiment, fusion bonding may be used. In anotherembodiment, a hybrid bonding may be used. In one embodiment the hybridbonding such as is disclosed in the above referenced related patentapplication is used. In another embodiment method, a thermocompressivebonding of metal regions may be used. In another embodiment, theback-end substrate is removed by grinding,chemical-mechanical-processing (CMP) or etch processes, leaving themetal layers bonded to the front-end substrate.

In an embodiment, the back-end substrate, which is processed without theneed for fabricating active devices, may be formed in a semiconductorprocess that differs from the semiconductor process used for the“front-end” substrate. The back-end substrate provides metal layersseparated by interlevel dielectric layers, which in an embodiment areformed in a less advanced semiconductor process, for example a 40nanometer wafer process, which provides a mature process, with lowermanufacturing costs; while the front-end substrate can be manufacturedin a very advanced semiconductor process, such as a 28 nanometer processor less. In this way the completed integrated circuit deviceadvantageously provides the advanced transistor performance of theadvanced semiconductor process, while the cycle time for the completeddevice is reduced by the parallel manufacture of the two substrates.

In various embodiments, the front-end substrate may includemetal-oxide-semiconductor (MOS) FET transistors that form complementaryMOS (CMOS) devices. In CMOS, n-type transistors and p-type transistorsare formed on a single substrate using, for example, oppositely dopedwell regions separated by isolation regions. In one embodiment, CMOSinverters are formed with a common gate structure extending over anN-well and a P-well to form a PMOS and NMOS transistor coupled togetheras a CMOS inverter, the CMOS inverter is a commonly used circuitelement. The active devices may include finFET and gate-all-aroundtransistors, capacitors, memory cells, image sensors, and the like.

The back-end substrate may have two, three, four or many more levels ofmetal separated and isolated from one another electrically by intermetaldielectric layers or interlevel dielectric layers, as is known in theart. The metals may include copper (Cu), aluminum (Al), aluminum copper(AlCu), nickel (Ni), aluminum germanium (AlGe), and alloys of thesemetals. In one embodiment copper metal conductors are used. Thedielectric layers may include oxides such as SiO2, nitrides such as SiN,silicon oxynitride (SiON), high-k dielectrics used in semiconductordevices, and low-k dielectric materials used in semiconductor devices.Vias, which are vertical openings are formed in the dielectric layersbetween metal layers are filled with conductive plugs or formed usingvia first or via last damascene processes and filled with conductormaterial in a plating operation.

The back-end substrate can include metal layers that in variousembodiments are formed by dual and single damascene processes. Indamascene, dielectric layers are patterned to form trenches. Conductivematerial is formed by electroplating or electroless plating to fill andoverfill the trenches. CMP is used with or without etching to expose thetop surface of the conductive material in the trenches, formingconductive lines. Additional layers are formed by depositing intermetaldielectric material and forming subsequent metal layers.

In an embodiment, fusion bonding is used. In fusion bonding, adielectric or oxide layer is polished to be very smooth, with surfaceroughness less than 10 Angstroms and in another embodiment, less than 10Angstroms and sometimes less than 5 Angstroms. When two substrates witha prepared surface of dielectric are placed in contact, bonding occurs.This fusion bonding can be performed with only slight pressure toinitiate a bonding process by physically contacting the two surfaces,and at room temperature. An anneal can then be used to strengthen thebonds, which may be very weak bonds initially. However, conventionalfusion bonding does not provide metal connections. Through via processesmay then have to be performed to complete the electrical connectionsbetween the bonded wafers by forming vias and filling them withconductor material, this is done after the fusion bonding processes arecompleted.

In an embodiment, a thermocompression wafer bonding can be used to bondmetal pads on wafers to form bonded wafers. In thermocompression, metalpads are bonded using mechanical pressure and high temperatures to causemetal bonding. The metal pads may be elevated above a dielectric layerby recessing the dielectric layer in an etch process prior to bonding,to improve the bonding process. Thermocompression bonding cansuccessfully bond metal regions, however, the high temperatures and highpressures required can cause additional defects and reduce yields in thefinished devices. Certain materials may not be compatible with the hightemperatures of conventional thermocompression bonding, such as advanceddielectric materials.

In another embodiment, hybrid bonding is used to bond the wafers. Inhybrid bonding, dielectric material is bonded in a manner similar tofusion bonding, and metal pads are bonded using an anneal process. Inthe related application incorporated by reference above, methodembodiments are disclosed for a hybrid bonding process where the metalpads are oxidized to form a metal oxide, the metal oxides are etchedfrom the metal pads, forming metal pads with well controlled surfaceprofiles, and the wafers are first bonded with a contact bond, and thensubjected to a relatively low temperature anneal to form metal pad tometal pad bonds. Both dielectric surfaces and metal pads bond in thehybrid bonding process.

FIG. 1 depicts in cross sectional view a portion of a semiconductordevice 100 that may be formed using the method embodiments. In FIG. 1, amultiple level metal structure is formed over a substrate to provide aCMOS integrated circuit. Layer 111 includes an active area on asemiconductor substrate, including transistors with source, drain, andgate regions, and vias connecting the transistors to a metal 1 wiringlayer. Layer 113 provides a metal 2 wiring layer. Layer 115 provides ametal 3 wiring layer. Layer 109 provides a top metal layer, whichprovides a top metal structure 107 for connection. Layer 109 furtherincludes a layer 103 for a pad 105. A passivation layer 101 is formedover the device and opened to expose pad 105 for external connections,for example by bond wires, solder balls, solder bumps, and the like.

The device 100 can be manufactured using a conventional CMOS process,and as described above, if that is the case, a long cycle time will beneeded to complete the device with the front-end process performed firston the substrate to form layer 111, and the back-end processes thenformed in sequence to form the remaining layers.

The embodiments provide methods using wafer bonding to manufacture thedevice 100 using reduced cycle time. This is accomplished bymanufacturing a front-end substrate and simultaneously orcontemporaneously, manufacturing a back-end substrate. The manufactureof the back-end substrate does not follow the completion of thefront-end processing and so it may be done in parallel, or even before,the front-end processing on the front-end substrate. In this manner thesteps that were performed sequentially in the conventional approach maynow be done in parallel and independently, increasing flexibility inmanufacture and reducing cycle time.

FIG. 2 depicts in cross section an example front-end substrate 111 foruse with the embodiments. In FIG. 2, a substrate 121 includes an activearea which includes isolation regions 123, which may be shallow trenchisolation regions, source regions 125, drain regions 127, which aredoped regions in the semiconductor substrate, gate regions 128 whichinclude polysilicon or metal gate conductors formed over a gatedielectric region, vias 130 that form vertical conductive connectionsbetween the substrate and metal 1, which is a conductive layer 131. Insharp contrast to the prior approaches, in the embodiments, thefront-end substrate 111 is only processed up to the metal 1 layer asshown. Because the layers of intermetal dielectric and the many metallayers above metal 1 are not formed on the substrate 121, damage such asPID defects is less likely, and yield is increased. In the embodiments,the cycle time to produce the front-end substrate is much shorter thanthe time to produce a conventional semiconductor wafer as the back-endprocesses are not performed on the front-end substrate.

FIG. 3 depicts in a cross-sectional view, a back-end substrate 150corresponding to the front-end substrate 111 of FIG. 2. In FIG. 3, acarrier substrate 151, which may be a silicon substrate, or othermaterial compatible with back-end processes such as a glass or ceramicsubstrate, is shown with metal layers formed in interlevel dielectriclayers above it. Note that in this non-limiting example embodiment, theback-end substrate is processed top-to-bottom, that is, the top metallayer 109 is formed on the carrier substrate 151, and the metal threelayer 115 is then formed, and finally the metal 2 layer 113 is formed.This arrangement is done in this embodiment so that the back-endsubstrate may be turned over, and aligned face down to the front-endsubstrate, and as described below, bonded so that metal-2 layer, 113, isbonded to the metal-1 layer on the front-end substrate 111 shown in FIG.2.

FIG. 4 illustrates, in a cross-sectional view, a wafer bondingoperation. The back-end substrate 150 illustrated in FIG. 3 is nowarranged face down and aligned with the face of front-end substrate 111.After alignment, the wafers are brought into physical contact. In anembodiment, the dielectric surfaces have been prepared to a smoothnessso that the dielectrics of the front-end substrate and the back-endsubstrate can form fusion bonds. An anneal process is then performed toform metal pad to metal bonds between the substrates. In variousembodiments, the hybrid bonding includes the methods of the relatedapplication incorporated by reference above, in which prior to bonding,both the substrates are subjected to an oxidation step to form metaloxides on the metal pads at the bonding surface for each substrate, themetal oxides are subjected to a wet etch to form uniform surfaces on themetal portions, and the substrates are then placed into contact, and athermal anneal of between 100 and 400 degrees C. is performed to formmetal pad to metal bonds, as well as dielectric or oxide-oxide bonds, inthe hybrid bonding process. In an embodiment, the metal layers arecopper, and the dielectric layers are silicon oxide. The metal oxidationprocess forms copper oxide, which is etched in a wet etch process. Themethod embodiments of this application are not limited to a specificwafer bonding process, however.

FIG. 5 illustrates in a cross-sectional view the structure 200 after thewafer bonding. In FIG. 5, the carrier substrate has been removed such asby backgrinding and a passivation layer 211 is shown with a pad 215 foran external connection. Comparing FIG. 1 to FIG. 5, it can be seen thatthe method embodiments have produced an equivalent structure to theintegrated circuit structure of conventional CMOS production used in aconventional process flow, however the use of the embodiments providesgreatly reduced cycle time.

It is noted that for fusion bonding between dielectric layers, thesurfaces are subject to a smoothness requirement. A low roughness isnecessary. While a typical CMOS semiconductor process may result in asurface roughness having a root mean square roughness of around 10Angstroms, for a fusion bonding interface, the surfaces need a roughnessof less than 10 Angstroms. In an embodiment, the surfaces of thedielectric layers at the bonding interface have a roughness around 5Angstroms. Further, for fusion bonding the surfaces should be morehydrophilic than a standard CMOS process provides. For example, in anembodiment the surface should have a contact angle of less than 15degrees for the fusion bonding.

FIG. 6 illustrates, in a cross-sectional view, an alternative front-endsubstrate 300 with a first layer 311, however in addition to thesemiconductor substrate having active areas, transistors, and vias, aredistribution layer is formed using insulator or dielectric layer 312and a metal pattern 314. The dielectric 312 may be a dielectric materialsuch as silicon nitride, in one embodiment. Other materials may be usedthat are compatible with fusion bonding. The metal redistribution layermay perform a “mapping” function and change the connection pattern ofthe devices in the underlying layer. Further the metal pads 314 may beof larger area than in the prior embodiments, providing additionalbonding structure. In an embodiment, copper metal pads are formed.

FIG. 7 illustrates, in a cross sectional view, a back-end substrate 350for use in a method embodiment with the front-end substrate 300.Back-end substrate 350 includes a carrier substrate 351, which may be asemiconductor substrate such as a silicon wafer, or another materialsuch as glass or ceramic that is compatible with back-end processes in asemiconductor manufacturing facility. As for the back-end substrate ofFIG. 3, above, in an embodiment the back end processing is performedfrom top to bottom, so that the layer 309 is formed on the carriersubstrate 351, and this is the top metal layer. The layer 315 is next,the metal-3 layer, the metal-2 layer 313 is formed next. In thisembodiment, a redistribution layer (RDL) 354 is formed over the metal-2layer, and, metal pads 352 are formed in contact with the vias of themetal-2 layer. The redistribution layer may perform a mapping function,moving connections from the underlying structure to new locations, forexample to change the connections for different versions of a device.The metal pads 352 are larger than the vias in the metal-2 layer andthus use of the RDL layers provide increased area for metal bonding.

FIG. 8 illustrates, in another cross-sectional view, a completedstructure 400 that includes the redistribution layers in the front-endsubstrate and the back-end substrates as shown in FIGS. 7 and 8, afterwafer bonding is performed. As described above with respect to FIG. 5,the structure 400 includes a passivation layer 411 and a pad 415 forexternal connections, the carrier substrate has been removed, forexample by backgrinding or CMP processes. The redistribution layer andmetal pads of this embodiment provide larger metal areas, increasing thebonding area for the wafer bonding. In an embodiment, hybrid bonding isused to bond the front-end and back-end substrates. In anotherembodiment, the hybrid bonding includes performing CMP on theredistribution layers to polish the insulator and to expose the metalpads, aligning the front-end substrate and the back-end substrate in aface to face relation, and contacting the faces to one another. Fusionbonding may occur on contact. A thermal anneal is performed to cause themetal pads to form metal bonds. In another embodiment, hybrid bonding isperformed using the methods disclosed in the related application,wherein the substrates are subjected to an oxidation to form metaloxides, the metal oxides are etched from the metal pads, leaving uniformsurfaces on the metal pads, the front-end and back-end substrates arealigned and brought into contact, where fusion bonding may occur betweenthe insulators of the redistribution layers, and the structure isannealed to cause the metal pads to form bonds.

In an alternative embodiment, the front-end substrate with theredistribution layer may be bonded to the back-end substrate with theredistribution layer using a thermocompression bonding. The variousembodiments are not limited to a specific wafer bonding method.

In various embodiments, the metal for the metal pads is chosen fromcopper (Cu), aluminum (Al), aluminum copper (AlCu), nickel (Ni),aluminum germanium (AlGe), and alloys of these metals. The metals areformed as damascene structures in a dielectric material. The dielectricmaterials in various embodiments is chosen from oxides such as SiO₂,nitrides such as SiN, silicon oxynitride (SiON), high-k dielectrics usedin semiconductor devices, carbon containing dielectrics such as SiOC,and low-k dielectric materials used in semiconductor devices.

In one embodiment, copper metal pads are formed surrounded by dielectricmaterial using a damascene or dual damascene metallization scheme onboth the front-end and the back-end substrates. Afterchemical-mechanical polishing (CMP) and planarization, the substratesare subjected to an oxidation process. In this example embodiment,copper oxide is formed using O₂ plasma. In alternative embodiments,other oxidation processes are used. A steam oxidation process such as insitu steam generation (ISSG) can be used.

In one embodiment, copper oxide removal is then performed by wet etchprocessing. In one embodiment, a dilute HF etch is used. In alternativeembodiments, the wet etch is chosen from etches including DHF at 2%concentration, HCl, HCOOH, and citric acid. In some embodiments, thetemperatures in the etch process are less than 250 degrees C.

Following the removal of the copper oxide, the substrates are inspectedfor copper pad profile match. The pads may be recessed slightly from thesurface of the dielectric material. The formation of the copper oxidefollowed by a well-controlled etch process reduces or eliminates thenon-uniform surfaces that result from the CMP processes, such asdishing. Control of the process allows for creation of slightly convexor concave surfaces on the surfaces of the metal pads.

By use of the embodiment methods, the copper pads have more or lessuniform surfaces. The front-end and back-end substrates with the wellmatched copper pad profiles are brought into alignment and placed incontact, with the dielectric layers in physical contact and the copperpads of the top and bottom substrates being spaced slightly apart.Slight pressure is applied to ensure the dielectric surfaces of thesubstrates are in good contact. Fusion bonding of the dielectric layersmay begin. Once the substrates are initially bonded, a relatively lowtemperature anneal is performed. During the anneal, the copper pads formbonds. The bonding between the dielectric layers will continue or bondstrength will increase during the anneal. When the copper pads are wellmatched and the metal pad recess depths are within certain predeterminedranges, robust copper bonds are formed and the substrates are bondedtogether; this is referred to as a “seamless” bond where the coppermaterial appears to be uniform across the bond interface.

FIG. 9 depicts in a flow diagram, an example method embodiment. In FIG.9, an integrated circuit to be manufactured is described at step 901 asa front-end substrate having one or more active devices formed therein,and a back-end substrate having connections formed as metal layersseparated by insulator layers, the metal layers corresponding toconnections to be formed to the front-end substrate. In variousembodiments, as described above, the front-end and back-end substratesmay include redistribution layers.

At step 903, the front-end substrate is processed. In an exampleembodiment, the front-end substrate can be processed at an advancedsemiconductor process node. Semiconductor process nodes are typicallycharacterized by the minimum feature size, or critical dimension, theprocess can produce. Often the minimum feature size is a minimum gatewidth for a transistor. An advanced semiconductor process node atpresent may be a “28 nanometer” process node, with smaller nodes such as20 nanometers, 16 nanometers, and so on in production or coming intoproduction.

The front-end substrate as described above will include one or more(often millions) of active devices such as transistors. In an embodimentthe transistor are CMOS transistors. Other types of transistors ordevices may be formed, including finFET transistors for example, or gateall around devices.

At step 905, and in parallel with and independently from step 903, theback-end substrate is processed. As described above, the back-endsubstrate is free from active devices and may be a ceramic, glass orother material that is compatible with back-end processing. The back-endsubstrate may also be a silicon substrate or silicon wafer. The back-endsubstrate, at step 905, may in one embodiment be processed in the samesemiconductor process node as the front-end substrate. In variousembodiments, the back-end substrate is processed at a differenttechnology node. In some embodiments, the back-end substrate can beprocessed at a less advanced technology node, which may save costs. Forexample, in an example embodiment the front-end substrate may beprocessed at a node of 28 nanometers, or less; while the back-endsubstrate is processed at a node of greater than 28 nanometers.

Also, the steps 903 and 905 can be done simultaneously,contemporaneously or in any order, adding schedule flexibility to themanufacturing process. When these steps are performed in parallel, cycletime is reduced over the conventional CMOS processing.

At step 907, the front-end substrate and the back-end substrate arebrought into face to face alignment and wafer bonding is performed. Invarious embodiments, hybrid bonding is performed. As described abovehybrid bonding forms bonds between the respective dielectric layers andthe metal pads of both the front-end and back-end substrates. However,fusion bonding, or thermocompression bonding, can be performed in otherembodiments to bond the substrates.

At step 909, the bonded devices are processed further in back-endprocesses such as solder bumping, wire bonding, packaging, to completethe device.

The front-end substrate and back-end substrates may be independentlymodified, adding design flexibility and the possibility of design reuse.For example, in an embodiment using the redistribution layers, the RDLlayers may map connections to the active devices differently, formingadditional variations of a design, without the need for redesigning thefront-end substrate.

Use of the embodiments advantageously provides methods to produce highlyintegrated devices with reduced cycle time, by using wafer bonding toform robust dielectric bonds and metal bonds between a front-endsubstrate with active devices, and a back-end substrate that is freefrom active devices. Advanced semiconductor processes may be used forthe front-end substrate, providing excellent transistor performance,while the back-end substrate may be formed in a less advanced, and lessexpensive, semiconductor process.

In an embodiment, a method includes defining an integrated circuitfunction using a front-end substrate having one or more active devicesand a back-end substrate having connections formed in metal layers indielectric material, wherein the back-end substrate is free from activedevices; manufacturing the front-end substrate in a first semiconductorprocess; more or less simultaneously, manufacturing the back-endsubstrate in a second semiconductor process; physically contactingbonding surfaces of the front-end substrate and the back-end substrate;and performing wafer bonding to form bonds between the front-end andback-end substrates to form a structure including the integratedcircuit.

In an example embodiment, a method is provided that includes defining anintegrated circuit function using a front-end substrate having one ormore active devices and a back-end substrate having connections formedin metal layers in dielectric material, wherein the back-end substrateis free from active devices; manufacturing the front-end substrate in afirst semiconductor process; more or less simultaneously, manufacturingthe back-end substrate in a second semiconductor process; physicallycontacting bonding surfaces of the front-end substrate and the back-endsubstrate; and performing wafer bonding to form bonds between thefront-end and back-end substrates to form an integrated circuit. In anadditional embodiment in the above method, the front-end substratecomprises transistors. In a further embodiment, manufacturing theback-end substrate comprises providing a carrier substrate; depositing atop layer metal layer over the carrier substrate; patterning the toplayer metal layer to form pads for external connection; forming apassivation layer over the top metal layer; forming an interleveldielectric layer over the passivation layer; patterning the interleveldielectric layer to form via openings; forming a metal interconnectlayer over the interlevel dielectric layer and filling the via openingswith metal; and continuing to form additional metal interconnect layersand interlevel dielectric layers to form a metal interconnect structure.

In yet another embodiment, in the above method, performing the waferbonding process further comprises growing an oxide layer over a topsurface of the front end substrate and growing an oxide layer over thetop surface of the back end substrate; performing an oxide etch toremove the oxide layers and provide a smooth surface on each of thefront end and back end substrates; and bringing the smooth surfaces ofboth the front end and back end substrates into contact for bonding.

In still a further embodiment, the method includes after the bonding,performing a thermal anneal to strengthen the wafer bond. In yet anotherembodiment, in the above methods the thermal anneal is performed at atemperature of between 100 and 400 degrees C. In still anotherembodiment, in the above methods, the first semiconductor process has afirst minimum feature size, and the second semiconductor process has asecond minimum feature size, and the second minimum feature size isgreater than the first minimum feature size. In still a furtherembodiment, in the above methods, the first and second semiconductorprocess have the same minimum feature size. In yet another embodiment,in the above methods, the first semiconductor process has a minimumfeature size that is equal to, or less than 28 nanometers. In analternative embodiment, in the above methods, the second semiconductorprocess has a minimum feature size that is greater than 28 nanometers.In still a further embodiment, in the above methods, the methods furthercomprise removing the carrier substrate from the back end substrate.

In another alternative embodiment, a method includes manufacturing afront-end substrate having a plurality of active devices in thefront-end substrate in a first semiconductor process; more or lesssimultaneously, manufacturing a back-end substrate in a secondsemiconductor process having connections formed in metal layers indielectric material, wherein the back-end substrate is free from activedevices; forming a redistribution layer over the front end substrate andthe back end substrate, the redistribution layer including metal padsand dielectric material separating the metal pads; physically contactingthe surfaces of the redistribution layers of the front-end substrate andthe back-end substrate; and performing wafer bonding to form bondsbetween the front-end and back-end substrates to form an integratedcircuit. In still a further embodiment, the method further includesperforming CMP on the redistribution layer of the front-end substrateand the back-end substrate to smooth the surfaces prior to physicallycontacting the surfaces. In yet another embodiment, the method furtherincludes performing a thermal anneal after bonding the front endsubstrate to the back end substrate. In still a further embodiment, themethod includes the metal pads that are one selected from the groupconsisting essentially of copper (Cu), aluminum (Al), aluminum copper(AlCu), nickel (Ni), aluminum germanium (AlGe), and alloys of thesemetals. In still another embodiment of the above methods, the dielectricmaterial of the redistribution layer is one selected from the groupconsisting essentially of SiO₂, SiN, SiON, high-k dielectric, carboncontaining dielectric, and low-k dielectric material.

In a further embodiment, a method includes forming in a firstsemiconductor process a front-end substrate comprising at least aportion of a semiconductor wafer and active devices formed within thefront-end substrate, and at least one metallization layer, and having afirst redistribution layer on an upper surface comprising metal pads anddielectric material between the metal pads; forming, in a secondsemiconductor process different from the first semiconductor process, aback-end substrate comprising a carrier substrate, at least onemetallization layer, and having a second first redistribution layer onan upper surface comprising metal pads and dielectric material betweenthe metal pads; smoothing the surfaces of the first and secondredistribution layers; bringing the first and second redistributionlayers into contact so that the metal pads of the front-end substrateand the back-end substrate are in physical contact; and bonding thefirst and second redistribution layers together. In yet a furtherembodiment, the bonding comprises thermocompressive bonding. In stillanother embodiment, the above methods include smoothing which furthercomprises performing CMP on both the first and second redistributionlayers to planarize the layers. In yet another embodiment, in the abovemethods, the smoothing further comprises forming an oxide layer on thefirst and second redistribution layers; and performing an oxide etch onthe oxide layer and exposing the metal pads of the first and secondredistribution layers.

Although the example embodiments have been described in detail, itshould be understood that various changes, substitutions and alterationscan be made herein without departing from the spirit and scope of theapplication as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, and composition of matter, means, methods and stepsdescribed in the specification. As one of ordinary skill in the art willreadily appreciate from the disclosure, processes, machines,manufacture, compositions of matter, means, methods or steps, presentlyexisting or later to be developed, that perform substantially the samefunction or achieve substantially the same result as the correspondingembodiments described herein may be utilized according to theembodiments and alternative embodiments. Accordingly, the appendedclaims are intended to include within their scope such processes,machines, manufacture, compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method, comprising: manufacturing a front-endsubstrate having a plurality of active devices in the front-endsubstrate in a first semiconductor process; manufacturing a back-endsubstrate in a second semiconductor process having connections formed inmetal layers in dielectric material, wherein the back-end substrate isfree from active devices; forming a redistribution layer over thefront-end substrate and the back-end substrate 350, the redistributionlayer including metal pads and dielectric material separating the metalpads; reshaping the redistribution layer over the front-end substrate tohave a convex surface; after the reshaping the redistribution layer,physically contacting the convex surface of the redistribution layers ofthe front-end substrate and the redistribution layer of the back-endsubstrate; and performing wafer bonding to form bonds between thefront-end and back-end substrates to form an integrated circuit.
 2. Themethod of claim 1, wherein the reshaping the redistribution layer isperformed at least in part with a oxidation process.
 3. The method ofclaim 2, wherein the oxidation process is performed at least in partwith an oxygen plasma.
 4. The method of claim 2, wherein the oxidationprocess is performed at least in part with an in situ steam generationprocess.
 5. The method of claim 2, wherein the reshaping theredistribution layer is performed at least in part with a wet etchprocess.
 6. The method of claim 5, wherein the wet etch process isperformed at a temperature of less than 250° C.
 7. A method, comprising:forming in a first semiconductor process a front-end substratecomprising at least a portion of a semiconductor wafer and activedevices formed within the front-end substrate, and at least onemetallization layer, and having a first redistribution layer on an uppersurface comprising metal pads and dielectric material between the metalpads; forming, in a second semiconductor process different from thefirst semiconductor process, a back-end substrate comprising a carriersubstrate, at least one metallization layer, and having a second firstredistribution layer on an upper surface comprising metal pads anddielectric material between the metal pads; smoothing the upper surfacesof the first and second redistribution layers, wherein after thesmoothing the upper surfaces of the first and second redistributionlayer at least one of the first and second redistribution layerscomprises a convex bonding surface; bringing the first and secondredistribution layers into contact so that the metal pads of thefront-end substrate and the back-end substrate are in physical contact;and bonding the first and second redistribution layers together.
 8. Themethod of claim 7, wherein after the smoothing the surface of the firstand second redistribution layer at least one of the first and secondredistribution layers has a roughness of less than 10 Å.
 9. The methodof claim 8, wherein after the smoothing the surface of the first andsecond redistribution layer at least one of the first and secondredistribution layers has a roughness of less than 5 Å.
 10. The methodof claim 7, wherein after the smoothing the surface of the first andsecond redistribution layer at least one of the first and secondredistribution layers has a contact angle of less than 15 degrees. 11.The method of claim 7, further comprising removing the carrier substrateafter the bonding the first and second redistribution layers together.12. The method of claim 11, wherein the removing the carrier substrateis performed at least in part with a backgrinding process.
 13. Themethod of claim 7, bonding the first and second redistribution layerstogether is performed at least in part with an annealing process. 14.The method of claim 7, wherein the forming the front-end substrate isperformed in parallel with the forming the back-end substrate.
 15. Amethod, comprising: receiving a front-end substrate; receiving aback-end substrate; converting a first portion of bonding surfaces onthe front-end substrate to a first oxide; converting a second portion ofbonding surfaces on the back-end substrate to a second oxide; performinga wet etch process on the bonding surfaces of the front-end substrateand the back-end substrate, wherein the wet etch process on the bondingsurfaces of the front-end substrate removes the first oxide and thesecond oxide and creates a convex surface on the first portion of thebonding surfaces of the front-end substrate; physically contactingbonding surfaces of the front-end substrate and the back-end substrate;and performing wafer bonding to form bonds between the front-end andback-end substrates, wherein the performing wafer bonding bonds a firstconductive region to a second conductive region and also bonds a firstdielectric region to a second dielectric region.
 16. The method of claim15, wherein the converting the first portion of bonding surfaces on thefront-end substrate to a first oxide is performed at least in part withan oxygen plasma.
 17. The method of claim 15, wherein the converting thefirst portion of bonding surfaces on the front-end substrate to a firstoxide is performed at least in part with an in situ steam generationprocess.
 18. The method of claim 15, wherein the performing the wet etchprocess utilizes dilute HF.
 19. The method of claim 18, wherein theperforming the wet etch process is performed at a temperature of lessthan 250° C.
 20. The method of claim 15, further comprising, before thephysically contacting the bonding surfaces of the front-end substrateand the back-end substrate, inspecting the bonding surfaces for padprofile match.